Direct or bulk incorporation and compounding methods are widely used in industry to treat polymeric objects with performance enhancing additives, resulting in the additive being dispersed throughout the bulk of the material. The term “additives” conventionally refers to chemicals and materials that are incorporated either into masterbatches or directly into resin mixes via direct compounding for bulk incorporation (additives for plastics) or into solutions for coatings (additives for coatings).
Reducing the amount of additives throughout the bulk of the polymer, however, results in a proportional reduction of the additive population at the polymer surface, which in many cases is where the additives' interactions with the environment external to the surface is most crucial. Thus, bulk incorporation methods are not particularly efficient at minimizing the amount of additives used to achieve a particular level of surface enhancement required from the material. Furthermore, additives at a surface of a material into which they have been mixed often have their activity or effect at least partially inhibited by the presence of excess material around them.
Bulk incorporation is inefficient in that while the goal of the method for surface enhancement is to produce a substrate having particles on the surface, a large number of particles are also dispersed within the substrate. Thus, in bulk incorporation, a large number of particles are effectively buried within the substrate and can not be presented to the environment exterior to the substrate. As a result, a comparatively large number of particles are needed to functionalize the surfaces of a given substrate by way of bulk incorporation. Also, achieving uniform dispersion of particles within the substrate is difficult, but may nevertheless be necessary for uniform surface area coverage of the particles.
In addition, melt-mixing polymers with their additives during bulk incorporation often necessitates high temperatures, which is energy inefficient, requires complex multistep processes to controllably heat and cool the polymer melt, can decompose the additives, or can unfavorably denature or damage the polymers themselves. Uniform and homogenous dispersion of the additives throughout the polymer bulk can be in many applications difficult to achieve in melt-mixing and other forms of mixing, as phase separation or particle flocculation and agglomeration may occur.
Surface coatings containing these performance enhancing additives may alternatively be used to achieve similar goals of modifying the surface properties of the substrate material. Surface coating methods, however, suffer from complex application and curing steps, thermal expansion incompatibility, peeling, and various other disadvantages.
Use of a coating process to make a functionalized surface can involve multiple additional manufacturing steps, including surface pretreatment, priming, and curing. Second, the coating layer must sufficiently adhere or bind to the underlying substrate so as to avoid detachment from the substrate, which is especially challenging for polymer substrates. Proper execution of coating-based techniques may require significant research and development commitments, and may also require additional primer layers or surface treatments. Third, the coating layers are generally substantially thicker than the dimensions of particles or additives, resulting in those additives being entrapped within the coating, thereby limiting their efficacy.
Accordingly, there is a need in the art for efficient methods of incorporating additives into polymers and polymer composite materials such as glass or fiber filled polymers so as to expose the additives at the polymer's surface but while also minimizing the amount of additives used. There is also a related need for methods for incorporating additives into the surfaces of coatings.